1. Field of the Invention
The present invention relates to computer networks in general and more particularly to methods for distributing information within said network.
2. Prior Art
The prior art abounds with computer networks in which server stations transmit data bases to other stations connected to the network. FIG. 3 is an example of such prior art network. There is shown a local area network (LAN) in which relatively expensive server station 2, which has a non-volatile storage unit 1 such as a disk or diskette unit enabling it to store programs without dissipating them, is connected through wiring 5 to a plurality of relatively inexpensive terminal stations 4A, ... 4N, which do not have such storage unit 1, but has memory units 3, the contents of which dissipate when the power is turned off. Such terminal stations 4A, ... 4N in the computer system can be used as terminal stations only when they are remotely initial-loaded with a program from server station 2 as soon as the power turns on. Thus, each of terminal stations 4A, ... 4N request the initial program loading from server station 2 when the power is turned on.
In the conventional initial program loading technique, there is a problem in that, even if terminal station 4B issues an initial program loading request while another terminal station 4A is performing the initial program loading, because the initial program loading can be performed by only one teminal station at a time, terminal station 4B must wait until another terminal station completes the initial program loading, and the initial program loading for terminal station 4B is started only when it is completed for another terminal station. Stated another way, initial program loading is done sequentially. Thus, even if a station requests loading while another system is being loaded, the requesting station must wait until the loading of the other station is completed. This waiting unnecessarily extends the time that a station must wait to receive an initial program load from a server station must wait to receive.
That is, as shown in FIG. 4, when terminal station 4A first issues an initial program loading request at time X.sub.1, a program is divided by frame (4 K bytes), and transmitted from server station 2 to terminal 4A. Every time the terminal station 4A receives a frame, it transmits acknowledge ACK to the server station. After it transmits the final frame, server station 2 transmits signal EOD, indicating the completion of program transmission, and terminal station 4A correspondingly transmits acknowledge ACK indicating the completion of initial program loading to server station 2. At this time Y.sub.1, the initial program loading is completed for terminal 4A. During this period, for example, at time X.sub.2, even if the user of terminal 4B turns on the power and requests the initial program loading, he must wait until time Y.sub.1, and then the initial program loading is performed until time Y.sub.2 by repeating the same steps as for terminal station 4A.
Therefore, if the users of terminal stations 4A and 4B turn on the power substantially at the same time, the user of the late terminal station 4B takes time (Y.sub.2 - X.sub.2) for the initial program loading that is about two times of normal initial program loading time (Y.sub.1 - X.sub.1). It is easily appreciated that, when N terminal stations are turned on at approximately the same time, the last station takes N times of the time required for the first one. Therefore, even when the initial program loading takes several seconds in normal time of (Y.sub.1 - X.sub.1) if ten-odd terminal stations are turned on at approximately the same time, the initial program loading for the latest terminal station takes several minutes in certain circumstances, which is unbearable in practical use.
It is not such a rare circumstance for a number of terminal stations to be turned on at approximately the same time. It is commonly encountered, for example, in the case where terminal stations are simultaneously turned on at the start of a company or a school.
Therefore, the solution of this problem has been important in the conventional initial program loading technique.